Linda Kloster - wife of the famous chess master Patrick Kloster - arrives at Monk's door, looking for help. She knows her genius husband is going to commit the perfect murder, and that she's the intended victim. Resigned to the fact that she's going to be killed, Linda only wants Monk to promise that he not let her husband get away with it. With Partick Kloster in Canada for a major chess tournament, there appears to be no immediate threat to Linda's life. Linda returns home, where she sends her maid for a cup of tea. By the time the maid returns, Linda Kloster is sprawled out on her bed, dead!
Monk, as determined as we've ever seen him, meets Patrick Kloster at the airport upon his return from Canada. Monk interrogates Kloster, but he gets nowhere. The medical examiner has ruled Linda Kloster's death a heart attack, and Monk can't prove otherwise. As explanation for his wife's death, Patrick notes that Linda was an alcoholic and heavy smoker for most of her life.
Monk, Natalie, and Julie visit a nearby park to talk to a young chess master who once played Kloster to a draw. The young master talks about the Poison Pawn - a chess move where Kloster dangles a pawn in the middle of the board. It's a trap - opposing players can't resist going for the pawn, and when they do, Kloster swoops in and crushes them. That's all Monk needs for a breakthrough.
Monk puts together a few clues from Linda Kloster's bedroom, and solves the case. Linda had secretly started drinking again. Patrick knew this, and poisoned her hidden bottle of liquor. Linda drank from it, then hid it herself. When Patrick returned from Canada, he had plenty of time to get rid of the incriminating bottle. With the evidence of a poisoning gone, Monk calls for a series of new toxicology tests on Linda Kloster's body. Unfortunately, Patrick is one step ahead of Monk - he's had his wife's body cremated.